This invention relates to the handling of cast concrete building products used in pre-cast and tilt-up construction, and more particularly, to a plug assembly for use with a coil insert which is embedded in the product and to which a hoisting means for lifting the product may be attached.
In recent years, pre-cast concrete products have been used widely by the building industry. Various building components, such as steps, may be cast in a mold and then transported to the construction site. In order to be able to handle these components easily, it is necessary to provide a means of attaching a crane cable to them. One or more inserts may be permanently embedded in the product for receiving a bolt-on lifting attachment.
A form of building construction referred to as the tilt-up method has also come into rather wide usage in which large concrete slabs are formed either on the floor of the building or on a level ground surface. The concrete slabs are then lifted into a vertical position and interconnected to form the walls of the building. Other types of building products may also be formed in this manner, such as columns.
The slabs are lifted by a crane, and a means of connecting the crane cable to the slabs must be provided. Generally an insert is permanently embedded in the slab, and lifting attachments, such as a lift ring and bolt, are attached to the insert. These attachments must be removable after the product has been lifted into place in order to provide a finished appearance for the building. Since the attachments are installed and removed at the building site, they are designed to be installed and removed quickly.
When the lifting attachments are removed from the slab or other product, a hole where the insert is located remains in the product and must be filled to provide a smooth surface. The insert should, therefore, be small enough to be concealed after the slab or other product has been installed, and yet should be sufficiently sturdy to sustain the forces of lifting heavy concrete products. Also, the insert should not interfere with rapid attaching and detaching of the lifting means.
Various types of inserts have been developed and are used in pre-cast and tilt-up building construction. One type of insert is designed to be positioned on the floor of the slab mold to provide a means of crane cable connection for lift-up construction. It includes several leg portions which hold a coil having a number of turns of heavy wire or rod stock. This coil provides an interior threaded opening in the top of the poured slab into which an attachment bolt may be threaded for lifting the product for tilt-up construction. The leg members are welded to the coil at the appropriate height above the mold floor so that the coil will be positioned just below the upper surface of the slab.
A number of different type of plugs have been designed to prevent access of fluid concrete to the interior of the insert coil as the concrete is poured into the mold. Among patents showing a plug with special characteristics for this purpose are U.S. Pat. No. 2,880,608, issued Apr. 7, 1959, to Boll et al, U.S. Pat. No. 3,216,171, issued Nov. 9, 1965, to Jenkins, U.S. Pat. No. 3,590,538, issued July 6, 1971, to Holt, and U.S. Pat. No. 3,742,661, issued July 3, 1973, to Tye. The plugs of all of such patents, however, offer certain disadvantages from the standpoint of both costs and simplicity of use.
Boll et al discloses the use of a filter plug described as composed of sponge rubber or some easily compressed rubber or elastic material allowing the plug to be inserted easily, and yet to be removed subsequently. Boll, however, does not teach how to insert or to remove the plug and, apparently, it would have to be crammed into the coil and, subsequently, dug out in piecemeal fashion. Each of the other three patents shows a two-part plug which must be separately threaded or otherwise fitted in place at opposite ends of the coil prior to installation, with the outer plug being removed after the concrete has set, but with the inner plug remaining in place for partial destruction by a coil bolt as it is threaded into the insert.
Another type of insert which is used primarily with pre-cast products is termed an edge pick-up insert. This type of insert provides a means of attaching a bolt to the edge of a product after the wood mold is removed. An edge pick-up insert has a coil for attachment to a coil bolt, such as described above. Edge pick-up inserts, however, generally do not have leg members but rather have a loop of wire which is welded to the insert coil. The loop insures that the insert is firmly embedded in the concrete. One or more such inserts may be fastened together by rods which are welded to the coils and extend between the inserts.
Since edge inserts of this type are designed to be positioned in the poured product with the coil adjacent a mold wall defining an edge of the product, means must be provided for holding the edge insert in the desired position while the product is poured. In the past, a plug having a threaded portion for engaging the coil has been screwed into the coil. the plug has then been nailed to the side of the mold wall and thereby provides the needed support for the associated insert.
In U.S. Pat. No. 3,889,916, issued June 17, 1975, to Ilukowicz, a protective plug for an edge pick-up concrete coil insert is disclosed which is made of plastic and is intended to be nailed to the mold wall. The plug has a threaded portion which is screwed into the coil and prevents concrete from entering the interior of the coil. A cavity is thus provided for insertion of a coil bolt after casting the product.
The plug of Ilukowicz is somewhat disadvantageous, however, since insertion and removal of the plug is time consuming. Additionally, the plug must be removed from the mold wall before it can be removed from the coil, since it can be removed only by being unscrewed from the insert coil. Every time a new concrete product is poured, therefore, the plug of Ilukowicz must be reattached to the mold wall.
It is seen, therefore, that there is a need for an improved plug assembly for positioning an edge pick-up insert in a mold as a concrete product is cast and for maintaining the coil of the insert free of concrete, but which plug assembly is capable of being inserted and removed quickly and easily from the insert. A need exists, as well, for a plug assembly which need not be removed from the mold wall after each product is cast.